C#写采集数据的程序，运用定时器

C#写采集数据的程序 ， 运用定时器每秒采集一次，需要采集的数据每0.5秒变化一次，我是菜鸟，求高手指导一下。

public partial class Form1 : Form
{

    System.Windows.Forms.Timer timer = new system.Windows.Forms.Timer(); 

    public Form1()
    {
        InitializeComponent();



        if (!serialPort1.IsOpen)
        {
            serialPort1.Open();
        }

    }


private void Form1_Load(object sender, EventArgs e)
{
        timer.Tick += new EventHandler(enviarPOLL);
        timer.Interval = 1000;
}

public void enviarPOLL(object sender, EventArgs e)
{

MessageBox.Show("Timer is running");//i set break point here. but it never get hit

}

private void serialPort1_DataReceived(object sender, System.IO.Ports.SerialDataReceivedEventArgs e)
{
try
{

this.Invoke( ( MethodInvoker ) delegate { timer.Enabled = true; } );

}
catch (Exception es) { throw es; }
}
}